Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Patent
1990-07-23
1998-03-03
Turner, Archene
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
20419212, 427160, 427162, 427164, 427165, 428212, 428336, 428469, 428432, 428433, 428446, 428697, 428698, B32B 900, B32B 702
Patent
active
057232075
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to infra red transparent materials. Such materials are useful as windows and lenses for thermal imaging systems, either as a coating or as a self supporting layer.
2. Discussion of Prior Art
Materials commonly used are germanium, zinc sulphide, and zinc selenide. All are relatively soft and therefore easily damaged. One method of protecting these soft materials is to coat them with a hard material. The coating most successful to date is a hard carbon that is diamond like in its hardness. This is described in GB 2,082,562 B. Disadvantages of this material are the interstitial graphitic inclusions which limit the optical transmission and the internal strain which prevents layers thicker than about 1 um being grown. An alternative coating of hard carbon includes a small amount of germanium to relieve stress and allow thicker coatings to be made; this is described in GB 2,129,833 A and its divisional 85 24,696.
Ideally a hard coating should be transparent in the 3-5 and 8-14 .mu.m infra red wavebands, and also in the visible band i.e. about 0.4 to 0.7 .mu.m. It is further desirable that the coating is stable and transparent at high temperatures so that it may be used as a window for high temperature processes. A disadvantage of the hard carbon, and hard germanium carbon coatings is their high temperature performance. On heating to say 600.degree. C. the carbon changes to a graphitic form which is absorbing to infra red radiation. These materials are also absorbing to visible light in useful thicknesses.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a material that is infra red transparent over a wide band of wavelengths and elevated temperatures.
According to this invention an infra red transparent material is formed of Zirconium nitride or Yttrium nitride also Cerium or Thorium or Europium nitride.
The material my be used as a coating on infra red transparent substrate material such as Ge, ZnS, ZnSe, AsS.sub.3, AsSe.sub.3 ; optically transparent material such as sodium, silica or lead glass; any suitable metal such as Cu, Al, alloys of Al, alloys of Fe or silvered surfaces; or as a self supporting layer in which case the supporting substrate is removed e.g. by etching. These infra red transparent materials Ge, etc., are transparent in the 1.9-2.7, 3-5 and 8-14 .mu.m wavebands. ZnS, ZnSe, As.sub.2 S.sub.3, As.sub.2 Se.sub.3 are also partly transmissive in the visible waveband. Glass is transparent up to about 2 5 .mu.m i.e. the visible and near infra red waveband. The coating is hard and may therefore be used for its abrasion resistant properties for example on infra red windows and lenses. Alternatively it may be used on metal to maintain a highly polished surface on components such as turbine blades and ductings. A further use on metals is to provide a hard wear resistant coating on cutting tools used on lathes etc.
The material may be formed by reactive sputtering using a target of Zr Y, Ce, Eu or Th in a DC or RF glow discharge of the gases Ar and N.
According to this invention an optical component comprises a transparent substrate coated with a transparent thin layer of ZrN, YN, CeN, EuN or ThN, the component being transparent in either or both the infra red (1.9-2.7, 3-5 and 8-14 .mu.m) and visible band (0.4 to 0.7 .mu.m) of wavelengths.
According to an aspect of this invention a machine tool cutting tip, turbine or pump blade is coated with an abrasion resistant coating of ZrN, YN, CeN, ThN or EuN.
According to another aspect of this invention the reflecting surfaces of a direct view thermal imager are coated with a thin layer of ZrN, YN, CeN, Thn or EuN.
According to this invention a method of producing Zirconium, Yttrium, Cerium, Thorium or Europium nitride comprises the steps: and 600.degree. C., a reduced pressure inside the chamber, cathode whereby argon ions sputter off material from the target to combine with nitrogen on the substrate and form the desired coating.
The glow discharge may be pro
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Lettington Alan H
Smith Colin
The National Research Development Corporation
Turner Archene
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